What are the radiographic features of eosinophilic granuloma?

Lytic lesions are common; the lesions may be ill defined or have sclerotic borders and are often multifocal. A periosteal reaction may be present.
Hole-within-a-hole sign: The outer table of the skull is more damaged than the inner table, which leads to the formation of button sequestrum.
Vertebra plana (i.e., complete collapse of the vertebral body) possible